The move represents a significant escalation in the fighting, which has already killed more than 40,000 civilians in a nearly two-year-old conflict that has threatened to destabilize the Middle East, and suggests increased desperation on the part of the Assad government. A fresh wave of mayhem struck the Syrian capital Damascus on Wednesday, reports from the region said, including a deadly triple bombing outside the Interior Ministry.

One US official, who asked not to be identified because he was discussing classified information, said that missiles had been fired from the Damascus area at targets in northern Syria.

‘’The total number is probably north of six now,’’ said another U.S. official, adding that the targets were in areas controlled by the Free Syrian Army, the main armed insurgent group.

It is not clear how many casualties resulted fromtheattacks by the Scuds — a class of Soviet-era missiles made famous by Saddam Hussein of Iraq during the first Persian Gulf war. But it appeared to be the first time that the Assad government had fired the missiles at targets inside Syria.

US officials did not say how they had monitored the missile firings, but US intelligence has been closely following developments in Syria through aerial surveillance and other methods, partly out of concern that Assad may resort to the use of chemical weapons in the conflict.

The Obama administration views the Assad government’s use of Scud missiles as a ‘‘significant escalation’’ of the conflict, said a senior official. It also shows, he said, the increasing pressure on Assad, since Scuds are primarily defensive weapons, being used by the government offensively against a counterinsurgency.

‘‘Using Scuds to target tanks or military bases is one thing,’’ the official said, speaking on condition of anonymity. ‘‘Using them to target rebels hiding in playgrounds at schools is something else.’’

Among other repercussions the Obama administration fears is the possibility that Assad’s military could fire Scuds near, or over, the border with Turkey, which has become one of the Syrian president’s most ardent foes. That could result in Turkey firing its Patriot anti-missile batteries, the administration official said.

Military experts said the Assad government’s use of Scuds might reflect worries that its aircraft have been vulnerable to rebel air defenses. In recent weeks, rebel forces have captured Syrian military bases, seized air-defense weapons and used some of them to fire at Syria warplanes. But one expert said that the government may have decided to use large missiles in order to wipe out military bases — and the arsenals they hold — that had been taken over by the opposition.

The Obama administration has yet to comment publicly on the missile attacks, but a senior administration official alluded to the development in a briefing for reporters Tuesday.

‘‘The Syrian regime has used aircraft,’’ the administration official said. ‘‘It has used artillery, and it appears that it has even used missile to attack the Syrian population and to attack what was a peaceful protest movement.’’

There have been other indications of Syrian government use of missiles. The Local Coordinating Committees, an anti-government activist network in Syria, reported from its Damascus office in an email late Tuesday that ‘‘Regime forces are firing land missiles that are capable of carrying chemical warheads.’’ The group did not elaborate on what the missiles were or where the information had originated.

The developments came as representatives of more than 100 countries and organizations that support the anti-Assad movement met in Morocco and endorsed a newly formed insurgent coalition as the legitimate representative of the Syrian people. President Barack Obama formally acknowledged that coalition, known as the National Coalition of Syrian Revolutionary and Opposition Forces, in an interview on Tuesday with ABC News.

But the leader of the coalition took issue with a decision by the Obama administration to classify Al Nusra Front — one of several armed groups fighting Assad — as a foreign terrorist organization and urged the United States to review that decision.

The coalition leader, Sheik Ahmad Moaz al-Khatib, said, ‘‘The logic under which we consider one of the parts that fights against the Assad regime is a terrorist organization is a logic one must reconsider.’’

He also said: ‘‘We love our country. We can differ with parties that adopt political ideas and visions different from ours. But we ensure that the goal of all rebels is the fall of the regime.’’

He was speaking after the Moroccan organizers of the conference said a declaration recognizing the new coalition as the legitimate representative of the Syrian people had been adopted by the 114 representatives at the gathering. News reports said the draft declaration adopted by the meeting also called on Assad to ‘‘stand aside’’ to permit a ‘‘sustainable political transition.’’

The document also warned against any use by government forces of chemical or biological weapons, saying such action would be met by a ‘‘serious response.’’ The Syrian authorities have denied that they will use chemical weapons against their own people.

In Damascus on Wednesday, a car bomb and two other explosives went off outside the Interior Ministry headquarters — known as the House of Justice — in Kafar Souseh, on the southern outskirts, Syrian state media reported.

Two Lebanese television channels that favor the Syrian government reported that there had been casualties. One channel, Mayadin, reported that the interior minister, Mohammad al Shaar, had been wounded, but other accounts said he had escaped unharmed. The other channel, Al Manar, run by the Lebanese militant group and political party Hezbollah, reported that four people were killed and 20 wounded.

An activist in Damascus, Abu Qays, said Syrian security forces had sealed off Shami Hospital, a central Damascus facility used by Syria’s elite, in a possible indication of high-profile casualties in the blasts.

The Kafar Souseh area has been heavily contested between security forces and rebels. Video posted on the Internet from the scene by Syrian activists showed several burned-out cars. A 67-year-old resident of Kafar Souseh, reached by telephone, said the explosion ‘‘shook the windows of my house.’’

Government forces and rebels have been clashing for two weeks around Damascus as rebels try to take control of the airport road and security forces try to seal off the capital from a semicircle of increasingly rebel-held towns reaching from the northeast to southwest of Damascus’ suburban sprawl.

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